There are some cases where dynamically loading code that your application doesn’t know about ahead of time can be useful. For example, perhaps you’re writing a text editor and you want it to be extendible via plugins. Or you are writing a library and you’d like your users to be able to provide their own integrations for 3rd party services. In any case, this pattern is very achievable in python.

For this post, let’s write a program that collects the latest top stories from various news aggregator sites like Reddit, Hacker News, etc. Let’s call it ubernews.py. We want to make it super easy for anyone who downloads UberNews to add their own modules for their favorite news sites. So UberNews needs to be able to access modules which aren’t part of it’s own codebase.

Since UberNews is pretty lame, it’s only going to ship with Reddit support by default. Once we have Reddit working, we’ll write a module for Hacker News (as if we were another developer) and load it into the main application.

First, some requirements. We’ll be making some http calls and since I’m not a masochist, we’ll be using the requests library, so make sure you install it into a virtualenv or have access to it globally.

Additionally, we’re going to explore some cool new features of Python 3.7, specifically Data Classes so make sure you are running at least Python 3.7.

Ok, let’s get started with a boilerplate ubernews.py:

{{< highlight python >}}

!/bin/env python3

from dataclasses import dataclass from datetime import datetime

@dataclass class NewsItem(): score: int title: str url: str time: datetime

class RedditNews: def get_news(self): return [ NewsItem(score=1, title=’test’, url=’example.com’, time=datetime.now()) ]

def main(): print(‘Top news for today:’) reddit = RedditNews() for news_item in reddit.get_news(): print(news_item)

if name == ‘main’: main()

{{< / highlight >}}

And the output:

$ ./ubernews.py
    Top news for today:
    NewsItem(score=1, title='test', url='example.com', time=datetime.datetime(2018, 8, 23, 17, 24, 8, 417234))

Let’s go through the members of this module.

First, we have the NewsItem dataclass. If you are not familiar with Python Data Classes, basically they are syntatic sugar for generating classes with auto generated methods, like __init__() and __repr__. Here we are simply using it do define a class with a few attributes, without needing to write a boilerplate __init__() function. We’ll get into some of the more useful features of Data Classes later.

Next we have the RedditNews class. It has a single method, get_news(). All it does is return a list of NewsItems, and for now a single, fake one.

Next, our main() function simply prints out a banner message and all of redditNews’s news items.

Let’s make this program actually do something: